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Thermometers - Digital vs Old School

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Hi All~

Well amidst my 72g project I have purchased 2 digital thermometers and have a large variance between the two I have a good 1.2 degree difference between the two. I would love to find something that is accurate. I was wanting to monitor the temp in my sump and in the tank. Haha maybe I am making too much of this but it just bugs me when readings don't match.

The two I have are a Coralife (the most accurate of the two but was .8 degrees high when tested spec says accuracy is +/- 1.5) The second is a Marina (it tested 1.2 degrees low I am sure it has a similar spec.)

Me too - I have one that suctions inside the tank to the glass. Not that people won't recommend digital ones though. Perhaps one of them is closer to a heater?

Nope I tested them both side by side in the same location. I also did a calibration test using crushed ice and water - this will yield a 32 degree temp to check the accuracy of a thermometer. The Marina gave a 30.9 degree temp and the coralife gave a 32.7 degree temp. I like the digital ones for readability. I might try to open one to see if there is an adjustment on the board.

I use an old school glass one as well. The only thing I don't like about it is that I feel like it takes it a long time to adjust the temperature reading. What I mean by that is, I use a gallon water jug to refill my ten gallon tank when I do a water change. Our water has a tendency to swing in temperature so I have to recheck the temp of each gallon jug and it seems like the thermometer takes a few minutes sitting to reflect the correct temp.
Does your digital themometer give an instant reading? I've been thinking of getting one for this exact reason. It won't hurt it to be off by a degree or two for waterchanges and it would be nice to have that peace of mind.

crunchy, I get annoyed with my old-school one for that exact same reason, but I'm actually reading the temp of the water coming out of the faucet for my water changes (using a siphon).

I typically place my glass thermometer on the opposite side of the tank from where my heater sits. That way I'll know the distribution of heated water is correct.

I've seen digital thermometers differ in readings from the old school variety, as well - same tank, different reading. I'm more akin to believing the old school one, because I never see variations of the same water with different glass thermometers. I'm sure they're reliable... just not "as" reliable. ;P

Glad I saw this thread with the pros/cons of the different thermometers. I honestly have never had a thermometer in my tank in it's 7 years. I was thinking I should probably pick one up eventually lol. I tend to rely on my heater because I have a Rena Smart heater that has different lights to tell me if my water temp is too high or low. I don't tend to worry about the temp difference in water changes because my tank is set to 75 and the general room temp in my house is 70-72 and I let my buckets of water sit and adjust to room temp before adding them to my tank and I have never had problems from fish stress. Is a thermometer really necessary?

I think they are very necessary unless you are in a region of the country where your temps stay consistent year round and you don't require a heater. While I do like to have something that is very accurate I mainly need it to determine that the temp is stable. The fact of the matter is that heaters do malfunction.... My light could be be green, indicating that all is good but the thermometer shows that the temp has dropped 5 degrees. I now know at a glance that something is amiss and needs attention asap. Well worth the $6 I paid for the thermometer.